Advent is the period of four Sundays and weeks before Christmas (or sometimes from the 1st December to Christmas Day!). Advent means 'Coming' in Latin. This is the coming of Jesus into the world. Christians use the four Sundays and weeks of Advent to prepare and remember the real meaning of Christmas.
There are three meanings of 'coming' that Christians describe in Advent. The first, and most thought of, happened about 2000 years ago when Jesus came into the world as a baby to live as a man and die for us. The second can happen now as Jesus wants to come into our lives now. And the third will happen in the future when Jesus comes back to the world as King and Judge, not a baby.
Christ has come, he has paid for sin, he has risen, and he is coming again! We have hope, love, joy, and peace in Christ.